As a communication system including a transmission unit, a communication medium, and a reception unit, in particular, a communication technique using a human body as a communication medium is called quasi-electrostatic field communication. In the quasi-electrostatic field communication, a user wears a transmission unit including a human-body-side transmission electrode and a space-side transmission electrode. The reception unit includes a human-body-side reception electrode and a space-side reception electrode. The human-body-side reception electrode receives a signal from the human-body-side transmission electrode through a communication path using a human body as a communication medium. The space-side reception electrode receives a signal through a communication path using a space as a communication medium. In the quasi-electrostatic field communication, only a user's touch on the reception electrode allows for communication. Utilization of the quasi-electrostatic field communication is expected, for example, in the field of security where door unlocking, etc. is performed.